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Producers are constantly faced with managing a wide range of animal diseases, of which botulism is one of the most common. However, it is possible to prevent and control botulism through annual vaccination.
According to Dr Janus van der Westhuizen of Morvet in Potchefstroom, botulism causes complete or partial paralysis in various animal species, including cattle, sheep, goats, horses, poultry and ostriches. Although it mainly occurs in cattle, sheep are also frequently affected. Botulism is not an infection, but a form of poisoning.
Causes of botulism
According to Dr van der Westhuizen, botulism is usually caused when animals ingest decomposed organic plant or animal material containing the Clostridium botulinum toxin. After ingestion of the spores, the bacterium can sporulate in the animal, during which the neurotoxin is then produced. This bacterium occurs and multiplies in rotting, protein-rich plant and animal material. The bacterium then produces the neurotoxin, or multiplies after the animal has ingested the spores, to form the toxin.
Animal material includes the carcasses of rats, mice, rabbits, turtles and birds, while plant material includes lucerne, among others. Baled silage often includes dead animals. Animals become infected when they ingest these dead animals along with other material, or when they consume neurotoxin-contaminated material. Botulism is not contagious; in other words, a sick animal cannot infect a healthy one.
The disease usually occurs during two scenarios. In winter, when the phosphate levels of rangeland tend to decrease, animals can develop pica. This entails an intense urge to chew on bones and turtle shells (osteophagy). The toxin, which is found in these bones and shells, is then ingested orally.
During wet conditions, Dr van der Westhuizen adds, the shell and legs of turtles can retain the toxin for a longer period, while the carcasses of turtles and other small mammals lose their toxicity after four to six weeks.
The second scenario is when the toxin contaminates stored feed if dead animal or plant material is present. Chicken manure can also contain the toxin. Other sources are water that is contaminated with carcasses or rotten hay and silage.
Symptoms of botulism appear between two and six days after ingestion of the toxin. Gradual paralysis is the most common symptom, says Dr van der Westhuizen. Muscles in the animal’s hindquarter are usually affected first, after which other muscles, including those responsible for chewing and swallowing, are affected.
Animals salivate excessively due to their inability to swallow. “As the disease progresses the forequarters are affected, causing the animal to lay down with its head on its side.” It eventually affects the respiratory muscles, which then leads to death.
He says that negative botulism test results are usually seen when post-mortem examinations are conducted, and that a diagnosis is generally made based on history, symptoms and the exclusion of other causes. Bones are sometimes found in the rumen, making botulism a likely suspect. For a definitive diagnosis, the toxin must be identified in the intestinal tract of the affected animal via laboratory testing.
According to him, cattle must be vaccinated against botulism at the age of six months. Four to six weeks later, they should receive a booster and thereafter they can be vaccinated annually. Where chicken manure is fed, vaccination is vital. In this case, animals must receive a second booster four weeks after administration of the first booster.
As is the case with other animal diseases, he says, preventing botulism is a better and cheaper option than treatment. In this regard, vaccination is essential.
Additional tips include the following:
- Make sure the feed is of good quality and is stored correctly.
- Frequently check that there are no carcasses in water tanks or dams, especially when birds have fallen into it. If possible, use a closed water system.
- Provide a phosphate lick in winter to prevent animals from developing a deficiency.
- Regularly search grazing camps for animal carcasses and old bones and remove them from the camp. – Christal-Lize Muller
For more information, send an email to Dr Janus van der Westhuizen at email@example.com.